A. Field of the Invention
The present invention relates generally to communication systems and, more particularly, to small world wireless ad hoc networks.
B. Description of Related Art
The use of ad hoc wireless networks has increased in recent years. An ad hoc wireless network typically includes several wireless, usually mobile, nodes. Each of the nodes includes an omni-directional antenna and communicates with only the nodes that are a single radio hop away. In such a network, each node acts as a router, forwarding packets of data from one node to another.
As the size of ad hoc wireless networks increase (i.e., to include hundreds or thousands of nodes), the problem of increased end-to-end transmission delays through the network results. Competing factors tend to make finding a solution to this problem difficult. These factors include the desire to transmit packets through the network at lower power and the desire to transmit packets through the network as quickly as possible.
Turning down the power on network transmissions maximizes spatial reuse of the radio frequency (RF) spectrum through the network. This low power transmission approach, however, gives rise to a network in which a given packet of data must take many hops from one node to another in order to cross the entire network, leading to a high end-to-end delay. On the other hand, direct, high power transmissions across the entire network are generally counter-productive because they result in a large area of radio interference and, hence, lower overall network throughput by eliminating spatial reuse of the RF spectrum.
FIGS. 1A and 1B are network diagrams that illustrate the single, high power transmission approach and the multi-hop, low power transmission approach, respectively. In FIG. 1A, a source node A turns up the power on its transmitter and transmits directly across the network to destination node B in a single hop. This high-power transmission causes interference over a wide area and leads to a corresponding reduction in overall network throughput because other nodes in the interference zone must keep silent during the transmission. As shown in FIG. 1A, the interference zone includes twenty-five blocked nodes. On the other hand, the single, high power transmission approach delivers the packet to its destination in just one radio transmission.
In FIG. 1B, the source node A uses a low power, multi-hop transmission. This series of small, hop-by-hop transmissions at low power results in better overall system capacity because it permits better spatial reuse of the RF spectrum. This multi-hop approach decreases the size of the interference zone over the single transmission approach. As shown in FIG. 1B, the interference zone includes twelve blocked nodes. On the other hand, the multi-hop approach requires a larger number of transmissions over the single transmission approach. Because the process of channel access takes time, as does the process of actually transmitting the data in the packet, an n-hop approach takes roughly n times as long as a 1-hop approach to deliver a packet from the source to the destination.
As a result, a need exists for a system that takes advantage of the benefits of the competing approaches while minimizing their disadvantages.